Cutting costs andtime with DFMAApplying Design For Manufac turing and Assembly

methodologies in early stages of produ ct design can redu ce th e

nu mber of par ts in a product and thus reduce cos ts.

By Steven Ashley, Associate Editor

The integr ati on of Boothr oyd Dewhurst's DFA software with Parametri c Technology's Pro/EN GINEER enablesa user to build a conceptual design as a three -dimensional solid model while simultaneously creati ng a DFAstructure chart complete with part names and dimensions.

SI \ I R \ I yL\R v .'\( ;U . Do uul.r-,Co uuucrcia l Ai rcr.i f Co. illLong Bc.u-h. Calif". LUI ' 0 111(.'

vimul .u io n -, of th eir tit-si gn .m d

m.umt.u-nmng operations [0 deter­mine wh .i t lin n 's t ill' costs o f ;I i l"­

li nn co nstru cti o n . T hL' CUlll p ,llly

di ' l()\,l'n ,d th.ir the costs of .rsscm­bl v. f.tbric.uiou. qua lirv ;\"SU LllI Cl' ,

and 1'\"l.' 11 ovcrhc.rd-e-invc ntorv k,'­1;' ]..;. tr.uking. and purch.i-iug-e-al ldepend 011 the p .Ub co un t.

ROll Suit er. gl.' lI L'r;l 1 1ll.1I1.lg l'r to raircr.ui 'y,rL' 1I1' .utd in tcrior dt', ign.it I)Ollgl.l "', .urd <cvcra l col league­were gin:1l the tack of finding ou twh.u cou ld be done to cn r rhcp.ur - co unt of ' 0 1111;' of th e com p.t­ny', pmducrv. Thev lined up can­did .uc, fo r product rvdcvicn .ui dav-cm blcd m nltid ic-ipl iu .rrv de ,i~1l

t l..' ,I111 \ th .it included dcvign l' 1l ~ i­

n vvrv . m.uiufacr urin g l' llg i lll' l·r,.

-hop Ilo o r mechanics. and <nppli ­cr n -p rc-cur.ui vcs. ;h \\'l·11 .1' <pv­ciali src i ll prod u ct io n ' lIp po n,m.unr.riu.rbilirv, and n -lt.ihi lu v,

Te.un mcm lu-rv were t.rughr I k \i gn f or I\ LlIluflCtli r i ll g.urd A" l' l11bly (I )F.\ lA) tt' l"i lll iqUl'\-,lIl exact ing dc-igu ­rev ie w me thod t h.u id en tifi c-, th e o p timal put dt'\i glLm .ncri .il- choice..md .I"l·mhly an d tabr ic.m o n opcr.uion­to p rodtu-c .m e tfi ci vn t .1I1 d rovr -c tfccrive produ c t.

" \\';ll king th ro ugh th e cx ivtinu lk'ig n in .1 n' ry \pl..·citlcproced ure pro mpted through out hy rhe I) F.\I A method ­o lngy. l'\T rybo dy star ted looking .u th e dl..' , igm ill ,I 11 1..' \\

wav," Su iter c.ud. " An,llyz ing eve r-y p.nt .m d o peration i ll;1 b,l,i c ,l,,",l..'lllh ly IIl.1h·, th e rc.un ri goroll\ly confront th eco mplexi ty o f ,I d l'\i gn .md work to ,i lll p l i t~ · it."

T Ilt' rc-uh- of th e D Ollgl.l, I)r~lA proj ect were imprcv­sivc. Sui ter <ud . O ne ' lI CCI..'''"' ' to ry \ \ ',1\ the rcd evign of theD ill ,IiI' door ,I\\l'mhly 011 th e ~ II )- 11. the t"lHllp,lIly" ,\{ II 1­

vc.tt .urlinc r. The original r.un .rir door ,1'\l'l1lh ly. ,1 p ,l "",,l g l'

th ro ugh w h ich outside- ,IiI' cuter- the c lhin ', .ur cond ition­

ing -vsrctu. \\"" .t long-sen'illg d l'\igll bor rowed trotu the

D ouglas DC- IO airliner. With 2 172 part s. the co m p lexdo or unit was considered difficult to install and ad just.

Simpl ifyi ng th e ram air door assembly des ign usingDH"l A techniqu es took abou t two week s. T he effort ledto a 36 pe rc ent redu c tio n in th e n umber of p;uts (to13H3), a 34 perce nt decrease in the numbe r of assemblyoperations (fro m 40 3H to 2()49). and th e elim ination of107 po unds, a significant mass reduction in an airplane.M oreove r, th e newly reco nstituted door un it design wassignific antly more reliable and easier to ma int ain . "T hereare fewer parrs to wear our," Suiter said. " Even th e uni t'sfu ncti on has improved ."

TYP I CAL RESULTS

The success o f Do uglas Com m ercial Aircraft in applyingDFMA practices to its designs is not unusual . Accordingto a su rvey of DFMA users con d uc ted by Bo o th roydDew h u rst Inc. (BDI) in Wakefield, R .I. , the fo remostdeveloper of DFMA strategies and software, typi cal resultsarc a 51 perce nt reductio n in part s co u nt , a 37 percentdecrease in parts cost, SOpercen t faster tim e-to-market , a()H percent improvem en t in qu alit y and rel iabi lity, a (12

percent drop in assembly tim e, and a 57 percen t reduc­tio n ill n u uu factur ing cycle tim e.

O ther use rs have achieved sim ila r results. " In mostcases, we end up with from 30 to HO pe rcellt fewer parrsan d fro m th ree to five more funct ions than pr ev io usly.depending on th e product ," said Sandy M un ro, principalin M u n ro & Asso c. ln c., a produ ct -design consu ltingfi rm in Troy, M ich ., an d another leader ill im plem entingI) F!'vlA techniques.

I)FMA, said Peter Dew hurst. dir ector of gradua te stud­ie s in manufacturing enginee r ing at th e U n iversit y o fR h od e lsla n d in Ki n g ston an d a p rin ci p al in BD !."makes o ne lo ok cr itically at the structu re of producr s­the relationsh ip between parts, th e nu mber of par ts. th esec uring m ethods- and try to design the assem bly co n­tent out of it while the design is still fl exible."

Th ough the division is so mewh at arb itrary, DFMA isgenerally split int o D esign For Assembly (DFA) and De­sign For M anufa cturing (DFM). In DFA. the key to 100\'ercost and im proving reliability is to produce designs withfe wer parr s. T he DFA approa ch also suggests w hen it isappropriate to design ori ent ing and insert ion fe atures intoth e part. In gelle ral, DFA focuses OIl parrs consolidation,top-dow n (gravity-ass iste d) assem bly, and co nce pt-s tagedesign review th rough team consensus. DFM , 011 the ot h­er hand, com pares the lise of selec ted mater -ials and m an­ufacturi ng pro cesses for th e parts of an assem bly, deter­m in es th e cos t im pact of those materi als and processes,and fi nds the most efficie nt use of th e compo nen t design.DI~A and DFM evaluate a design by roughly estim ating

th e reso urces and effor t ne ed ed to b uild th e prod uctbased on industry average estim ates . Ikwh urst said . T hiskind of "scorekccping" allows direct com parison amongdesigns. Fo r ex am ple, reducing the number of parts maysim plif)' the entire assembly, but co m bining several fuu c­rio ns ill on e co m po ne n t co u ld result in a co m plicate dpart th at is pro hibitively expe nsive to manufacture. M ore

typi cally, however, the cost o f prod ucing extra features ono ne part is m uc h less th an th at o f p ut ting th ose featu reson separate parrs. T hus, DI:MA allows for diffe rent designscenarios. By see ing the result s up from , D ewh u rst said,one can ge t th e m ost out of each m ater ial and pro cess.

T he m ethodology, said David M eeker. pr in cip al eng i­neer at the Systems Business Technology unit o f DigitalEq u ipment Corp. in M ayna rd . M ass.. m akes the teamphysically and syste m atically walk throu gh th e d esignand talk about its advan tages and sho rt co m in gs, whi chcom pe ls clear decisions o n rradc- otl s. " It also f()f(..'es youto keep go od design reco rds, w hich are useful dow n th eline." M eeker adde d. By th e en d o f a DFMA pro cess. astep-by-s te p descriptio n o f th e ag reed-upo n m auu fa c­tu ring and assembly process has been writt en dow n.

BEYOND KEEPING IT SIMPLE

When com pute r- aide d design (CAl )) technology was de­vclopcd . Dew hurst said . design engineers acquired pow­ertul quantitative an alyti ca l to ols that provid ed the basisfor making a judgement of a design 's perfo rmance. " UntilI)FMA came around, manufacturing engin eers didn't havesim ilar quantitative tools. The qu alitative evaluat io ns thema nufa cn uing engine ers had to o ffer ill ;lllY discu ssio nsdi dn 't carry mu ch weight when th e d esign ers had rea lnumbers from CAD upon which to base th eir decision s."

" M anu fac tu r in g tech n ol o gy h as improved over th eyears, but no t necessar ily in th e mi nd of the design eng i­neer, who is typi cally used to applyin g th e ' Keep It Sim ­ple. Stupid' approa ch ," said Mel H unter. corporate m an­ager of cost improvem en t at Em erson Electr ic C o. in St.Louis, Mo. " H oweve r, more co m plica te d pa rt s capa bleof fulfil ling several funct ions usually m ean using a d iffer­ent ma nu factur ing pro ccss. Df MA allows one to estimateth e cost ramifi cat ions of that cho ice ."

DFMA is a way to get away from traditional product de­sign practices, in which deep- seated habit s 0 11 th e part ofrhe design engineers lead to seque nt ial eng ineering . cre­at io n of single- fuucnon parts with ma llY fasreuers. andth e iteratio n of multiple pro duction models. It also helpsavo id the in teror g.uuzation al and int erdi scipl inary pro b­lems that ofi eu plague new product teams.

T he techn ique has gained popularity as a benchmarkingtool becau se it helps define the design and nunufacrurm gcap .rbilirics ofcompcri rors and their cost- to -nu rkct -enn-vtar gets, as we ll as pro viding compa r-iso ns to com pe titors 'pro ducts, M eek er said. But DFMA call go eve n beyondthose tasks, Dew hurst said. " We realized it was a couuu u­nicnti on tool tor te.uuworkiug. Ha ving arisen at the sametime as th e movement toward co nc u rrent eng inee ring.DFMA provi des a focu , for th e d iffere nt organi zat io nalcultu res represented by the team members."

Thou gh th ere a re seve ra l d iffer in g va ri e ri es of th eDFMA m crhodologv, th e ge ne ral co ncep t behind all o fth em originated in Britain in th e late 1970s, wh en man­u fac tu r in g resear chers were in vest iga ting \vays to rc­design produ cts so th ey co uld be easily assem bled by ;1tI ­

rotuated equ ipme nt . Soon it was realized that this workwas lead ing to 'a set o f guidelines that wou ld point prod-

:>.HT llAN IC A I I'.N C I :-.JU ' R I N C ",I AR C II 1' )'1 .:; 7 5

uct design ers toward design s tha t wo uld be easier to

build ill general. But w he n Br-i tish industry failed to sup­port the new research , th e co nce pt ende d up bein g ap­pli ed initially in th e U nited Sta te s. UDI introduced itsfirst Il FA software in l Y81 in response to requests fromearlv practitioners, incl uding electrical co nnecto r-ma kerAJ\l P Iuc.. Di gital Equipment C orp.. G en eral ElectricCorp.. We\ tingho use Electric Co.. and Xerox Corp.

In the B1 )1approach (w hich is represen tative of others),several qu estions arc asked about each part in a productdesign : D ocs the pa rt m ove wit h respect to the ot herparts already assemblcd? M ust th e part be made from ad ifferent mat er ial o r isolated from all the other parts al­ready a...sembled? M ust th e part be separate from all ot he rparts because assembly or disassem bly wo uld othe rwise beimp ossible? These questio ns lead the reviewers to n -cval­uate each part and process that has been specified.

" T he idea is to get away from piece-functional designand move toward syste m- func tio nal design . w hich im­pro vcs system efficien cy' Sandy M UIln> said . H is compa­ny 's I>FMA approach pro mo tes a ser -i es of "good designpr incip les" related to DFMA: I . USt' teamwo rk. 2 . M ini­mize the number of part s. 3. Design so the assembly canproceed in a layered fa...hion from above . -l. Design matingparts that are t'asy to insert and align . 5. Avoid expe nsivefasteni ng operations. 6. 1k sign out hand ling problems-

After Dougla s Aircraft enginee rs redesigned the ex isting waste pipe andwire harness bracket on the MD·9Q airliner (left) using DFMA procedures.the unit's part count dropped from 15 to 3, assembly operations were cutfrom 210 to 8, assembly time decreased from 46 min. to 3 min., weightwas reduced from 2.1 oz. to 0 .8 oz.• and tota l product cost was loweredfrom $64.01 to $4.74 (rightl .

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go for bulk sto rage. 7. Design for " Po ke Yoke" o r erro r­proof assembly H. Design th e p:uts to affix them selves oneto ano the r. <J . Sim plify se rvici ng and pack agin g. 10 .Eliminate adjustments and physical reorientation s.

GETT ING MANAGEME NT ON BOARD

IJcspite the relative success of I)FMA it remains a woefitllvuud cru sed tool. said consultant Rob Carr inger. senior vicepresident of the George Group Inc. in Dallas. " By the timeth e lit-sign is in manufactu ri ng, about SO perc ent o f thecost is locked in , but it's hard to tackle the root causes."

Although everyo ne in product t'ngineering is aware ofthe ben efits o f DFMA, Bill Sprague . BDI's vice presidentof implementation services, said th at few have bo ughtint o th e full-fledged process changes it dem ands or livedth rou gh it so that th ey tr uly understand its pot ential.

Emerson 's Iv1e1 H unr cr said th at unl ess managem ent iseduc ated about th e DFMA approa ch, and co mmitted to

the proj ect , it will fail. "They have to put th eir bacon onth e line to ensure there is no co nflict between part s ofth e organiz at ion . Man agem c ur also has to se t asideeno ugh tim e for th is fu ndamental change to take place.It do esn 't happen instantly,"

Assembling and manag ing the interdi sciplin ary produ ctdcsign team is also no small o rde r. ""A lot of co mpaniesjust throw a bu nch a peo ple together," M eeker said . " O f..ten th ey don 't pull together and wo rk for th e co mmongoa l, because managem ent do esn't g ive them eno ugh au­thority or co ntro l over w hat th cv are doi ng." He addedthat managem ent must also reward th e team as a w hole.

T hen the re are the personal dynam ics involved . All ofthe team members. M unro said, " have to adm it to them­selves that they cau'r do it all by them selves. for team workis the key to success. Using DFMA in a vacuum will yieldlim ited results because no one knows everything .'

Early o n, it is useful to give the team structured tasks tospark crearivirv and to ge t members used to working to ­gethe r. " J)FMA pro vid es a nonthreat ening way to getpeopl e talkin g abo ut a design witho ut feeling like othersarc encroaching o n the ir territor y," said J im 'Ibut , dire c­tor o f design eug iuec ring at roy tu aker H ashr o Inc. inPawtucket , R .I. , w hich has succe ssfu lly app lied J>FMA to

several products.It is also essent ial to ge t hands- on kn owl ed ge from

th ose o n th e sho p floor and fro m installers [0 tr uly un ­dervtan d the probl em.. wi th th e existing design . M arrydesign engineers say they had no idea how mu ch wo rkpe opl e go throu gh to put t h ci r produ ct s to gether."When peopl e really understand th e other team mem­bers' requiremen ts. it removes most of rhe subjectivity orrivalry from the decisio n-making pro cess," Sprague said .

Con vinc ing reams to rely on the cost and cycle tim e es­rimatcs for eac h design choice is also a problem . " N o­body trusts what you say on face value : ' Munro said." T hey want to sec w he re those cost and time estimatesco me from. The estimates have to have eno ugh credibil­ity fo r peop le to buy into th e program . In fact . the ent ireissue of choosing metr ics is important because di ff erentkinds of scorekeeping lead to diflerenr result"."

Following a DFMAdesign review by Hasbro engineers, the ladder assemblyon the Tonka Talk n' Play Firetruck was redesigned in plastic, the numberof components was reduced fr om 33 to 5, and assembly ti me droppedfrom 198 to 22 sec.

T here is also so me di sp ut e abo ut wh eth er everyt h ingshould be boiled down co cycle times and money. "I thinkit's a big m istake to calibrate every thing in terms of do llars,"said Mel H unter, " beca use it allows people to twe ak thefigures to push the analysis in on e direction or another."

Sprague said that there is a need to calibrate the analysismetho ds to the spec ific activities of th e part icular organi­zat ion and the industry to mak e su re tha t th e terms me anso me th ing to them. Fo r ex am ple, in most D FJ\l A sys­tem s, th e ma nufactur-ing eng ineer e m set up preferen cesto fit the o rgani zation 's syste m o r enviro u m en t-c-t ' th etypc of tools yOll use, the d istance s yOli move. and soforth ," Spra gue said . In gene ral. the erro r associated withthe cost and tim e estima tes is in the range of S to 10 per­cent, " Ifth ere is a discrepancy, it 's usually because certainaspects o f the process are being ignored." he said.

DESI GNIN G FOR CU STOMERS ' OPERATION S

T he next frontier for DFMA lllay be de signing product sfor effic ient use in the custo mer's manufactu ring op era­tions, acco rd ing to Pet er M arks, ma nagin g d irect or o fDesign Insight in Los Cntos, C alif. As pan of a survcy o fthe best design and manufacturing pract ices, he foundth at com pan ies like AM P were designing their connec­tors no t j ust for man ufacturabilirv in their own plants butfor com patibility w ith the custo mer's operations. Sim ilareffo r ts, M arks said , we re taking place at Ko dak (fast pho­to labs, digital imagin g), General Electr ic Aircraft En­gin es (easie r integr atio n wi th airframe d esigns), H arr is(faste r p rint job chan ge overs ). and Kenn cmeral (o pt i­m ized tool select ion and managem ent ).

1\;10st cut -rent DFM A pro grams are followed using so fi­wa re developed for the pro cess. "Software is cruc ial to

en fo rcin g struc tu re and add ing rigo r to th e pr oj ect ,"Spragu e said , " T he re are to o man y var iables to keep inyour head , and the software collec ts all th e data,"

n r:MA software is provided by UD!. Lucas Engin eering &­Syst em s Ltd . in Sol ih ul l. U. K. (d istr ib u ted in N o rt hAm eri ca by Munro }, and Sapphire I)esih:rtl System s Inc. inPalo Alto, Calif. " Each system has the same mission ," saidM eeker. " they j ust do it differently or to different degrees."

O ne no table recent development Ius been th e int egra ­tion of UUI's DFA package in to Pro / EN(; IN EER fromParametr ic Techn o logy Corp, ill Walt ha m, Ma ss. Th eintegrnte d syste m allo ws feature d imensio ns and partslists bui lt into the solid model to be auto ma tically dow n­loaded into DFA files. An engineer can build a co nce ptu­al design as a th ree-d im ensional mo del and automaticallycreat e a Dr:A structure ch art , com ple te with part s nam esand dimen sions . ready fo r sim ultane o us design revi ew.

BI) I also o ffers DFM cost-esti mating modules for severalmanuf acturing processes, including machining. shee rme talwo rking. inject ion molding, powder metal fo rming. anddie casting, f or exam ple. BDI recently released M achi nin gfor Windows. versio n 2, wh ich derives mach ini ng timesand costs to r co nc ept-stage design s. Based on econo micmodels of the pro cesses, these DFM tool s permit eng inee rsto calcul ate the cost savings resultin g from easier assemblyversus the adde d co st o f more co m plicated to oling andot her process factor s for a more co mplex part.

A success fu l exam ple of these DFM capabi liti es to o kplace ;1£ H asbro. T he largest toy com pany in the world isusing D[= J\.l A to identify design aud cost improvem ents atthe w ry earli est co ncl'pt stages of design .

Toy retailers do nor want to carry inven tories. said Ji mTo ur. " Because tim ing is so critical, till' em phasis is ongett ing pro du cts shippe d o n sche dule, DFMA is a big partof th is movement because it helps eliminate pro blem s illthe de-bu g producti o n sta rt - u p p ro cess by analyzin gpart s co unts, asseil lbly times. and mater ial cos ts before ad esign co ncep t is lo cked in and cha nges becom e tootim e-consum ing to implement ,"

Cost wa s the challenge for the Ton ka Tal k n ' Pla yPircn-uck , one of H ashro 's successes o f the I<J<J3 Christ­mas seaso n , Afte r DFMA ana lysis. it became clear thatcosts could be red uced if the traditionally metal firerruckwe re redesigned in plastic.

T he red esign invol ved moving the ligh ts from the frontcab to th e rear assembly, changing aesth etics, co m biningso me parts, and el im inatin g m any fasteners. T he bi gchange, howe ver, was to th e ladder assem bly, explaine dHa sbro proj ect engineer Pat Egan . The or iginal ladderwas com posed. of a tota l of 33 parts and assemblies, w ithan assembly time of 19R seco nds. T he redesigned ladd erbrought the num ber of part s down to its th eoretical min­innuu of o nly five. all plastic. w ith all assembly time ofjust 22 seco nds, " It looks as n ice as th e metal assemble.and it performs the same fu nction s," Ega» said . " Plus. it 'smore reliable wh en subjected to abuse-testin g ." In addi­tio n , th e toy tru ck met its cost targets.

DH\;lA consul tan ts are typ ically brought in as a last re­so rt , Sp ragu e said, wh en a co m pany w ants to up g rad eproduct-devel opm en t capabilities to tig ht it s co m peti­tion , o r when it has specific cos t obj ectives for a productco nside red to be cr itical to the co m pany and n r:M A isth e onl y way to do it. T he "lu xury of ad versi ty," howev­er, should not be the pri me reason to adopt n r:MA prac­tices, Einstein on ce said th at " the best design is the sim­plest one that wo rks." DFMA provides the ch eapest wayto reach tha t go al. •